Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1990-01-17
1990-11-20
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
356357, 356382, 250226, G01B 1102, G01B 1106, G02F 101
Patent
active
049720724
ABSTRACT:
Circularly polarized light is used to detect an end point of a thin film layer. Collimated light is passed through a polarizing filter and a polarizing beam splitter resulting in light which is almost entirely linearly polarized in a first direction. This first direction polarized light is passed through a quarter wave retarder and is converted to circularly polarized light. The circularly polarized light is reflected off of a surface having a thin film layer and passes back through the quarter wave retarder. This reflected circularly polarized light is converted by the quarterwave retarder into linearly polarized light having a second direction. This second direction polarized light is easily isolated by passing it back through the beam splitter. The light may then be analyzed by end-point detection circuitry and the end-point of the film layer detected.
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Hauser Hugo
Monahan Kevin M.
Messinger Michael
Nelms David C.
Schatzel Thomas E.
Tritec Industries, Inc.
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